Nevus (or naevus, plural nevi, from nævus, latin for birthmark) is the medical term for sharply-circumscribed[1] and chronic lesions of the skin. These lesions are commonly named birthmarks and moles. By definition, nevi are benign. Histologically, nevi are differentiated from lentigos (also a type of benign pigmented macule) by the presence of nests of melanocytes, which lentigines (pl. form of lentigo) lack.
Melanocytic nevus (nevomelanocytic nevus, nevocellular nevus): benign proliferation of melanocytes, the skin cells that make the brown pigment melanin. Hence, most nevi are brown to black. They are very common; almost all adults have at least one, usually more. They may be congenital or acquired, usually at puberty.
Epidermal lesions:
Epidermal nevus: congenital, flesh-colored, raised or warty, often linear lesion, usually on the upper half of the body.
Nevus sebaceus: variant of epidermal nevus on the scalp presenting as a hairless, fleshy or yellowish area.
Connective tissue lesions:
Connective tissue nevus: fleshy, deep nodules. Rare.
Vascular lesions. See birthmark for a more complete discussion:
Blue Rubber Bleb Nevus Syndrome: dilatation of veins anywhere in the body (both skin and internal organs), usually lethal from internal hemorrhage. It is a very rare genetic disorder.
